Structural Diagnostics : Assessing Fire Damage

Dudley Engineering is experienced with assessing foundations which have been exposed to fire damage. When assessing a foundation exposed to a fire we look for the following visual cues:

  • scorch marks
    • Smoke stains and scorch marks are typically good indicators of areas that were exposed to high heat and require further evaluation (see sounding hammer below)
  • cracks
    • Concrete exposed to high heat and then subsequently doused with water as is typical in a normal structural fire, can lead to drastic temperature changes and hence quick expansion and contraction of concrete leading to cracks. Consider placing a glass in the freezer and then subsequently removing it and running hot water over it, it will crack (not that we have ever done that before).
  • changes in color
    • A change in the color of the concrete may indicate that the concrete was exposed to heat exceeding 550°F. Concrete exposed to temperatures above 550°F often turn a shade of pink which indicates that a chemical change has occurred in the iron-containing aggregates and cement paste.
  • surface spalls
    • High heat can cause the pore water in the concrete to evaporate which can lead to spalling of the concrete.

Our assessments also include testing of the concrete via a sounding hammer. A sounding hammer can be used to compare the resonance of the concrete after it is struck by the hammer. Healthy concrete will exhibit a sharp, high-frequency ringing sound when struck, while damaged or poor-quality concrete will typically exhibit a dull thud or soft noise.We, in corroboration with may documented cases, have found the sounding hammer technique to be a reliable and cost-effective means of assessing damage to concrete in the wake of a fire. The sounding hammer can also be used for destructive testing to assess the strength of the concrete. Healthy concrete will be unphased by a couple blows from a sounding hammer while heat-damaged concrete will crumble away with a few rigorous hits. Additionally the fracture mechanics of heat-damaged concrete is unique in that the fracture plane will typically form around the aggregate as opposed to directly through the aggregate, which is characteristic of healthy concrete.

Chalky Cement Paste – Indicative of Heat-Damaged Concrete
Spalling Concrete with Pink Color Tones – Fracture Plane Around Aggregate Pieces
Pink Color Change of Concrete